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United States Patent |
5,255,134
|
Sekiya
,   et al.
|
October 19, 1993
|
Auto-tracking system for magnetic recording/reproducing apparatus
Abstract
An auto-tracking system for a helical scan type magnetic
recording/reproducing unit comprises a synchronizing signal separating
circuit from video signals on a running magnetic tape reproduced by a
rotary video head, a periodicity variation measuring and comparing circuit
in the synchronizing signals separated in the synchronizing signal
separating circuit, and a tracking control means which controls the
running condition of the magnetic tape with reference to a phase
difference between a reference signal in association with the rotary video
head and a signal representing the running condition of the magnetic tape
and changes tracking by a predetermined amount in response to the
periodicity variation measured by the measuring and comparing circuit so
as to minimize the periodicity variation measured by the same, thereby an
optimum tracking position is obtained without being interfered by
cross-talks between the adjacent tracks.
Inventors:
|
Sekiya; Masataka (Ibaraki, JP);
Hiramatsu; Kiyoshi (Ibaraki, JP);
Usami; Hideyuki (Ibaraki, JP);
Ohta; Hisashi (Ibaraki, JP)
|
Assignee:
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Hitachi, Ltd. (Tokyo, JP)
|
Appl. No.:
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700843 |
Filed:
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May 16, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
360/70; 360/73.07; 360/77.13; 386/87 |
Intern'l Class: |
G11B 015/467; G11B 021/04 |
Field of Search: |
360/70,73.07,77.13
358/321,338
|
References Cited
U.S. Patent Documents
3845500 | Oct., 1974 | Hart | 360/77.
|
4210943 | Jan., 1980 | Nakamura et al. | 360/70.
|
4255768 | Mar., 1981 | Kubota | 360/77.
|
4607298 | Aug., 1986 | Yamashita | 360/73.
|
4920435 | Apr., 1990 | Yamazaki | 360/70.
|
5119246 | Jun., 1992 | Tomitaka | 360/70.
|
Primary Examiner: Zazworsky; John
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus
Claims
What is claimed is:
1. An auto-tracking system of a helical scan type magnetic
recording/reproducing apparatus in which a run of a magnetic tape is
controlled by a signal representative of a phase difference between a
reference signal and a signal indicative of a running phase of said
magnetic tape, comprising:
first means for separating a synchronizing signal from a video signal
reproduced by rotary heads of said apparatus;
second means for successively measuring periodicity of said synchronizing
signal of said video signal obtained in a field or frame and comparing the
measured periodicity with a periodicity measured for a preceding field or
frame to provide a variation of periodicity of said synchronizing signal;
servo means responsive to said signal representative of said phase
difference for controlling a running state of said magnetic tape; and
tracking adjust means responsive to said periodicity comparison in said
second means for causing said servo means to successively change tracking
by a predetermined amount such that the periodicity variation measured by
said second means is minimized.
2. The auto-tracking system claimed in claim 1, further comprising third
means for disabling said tracking adjust means when said periodicity
comparison in said second means indicates an equality.
3. The auto-tracking system claimed in claim 2, further comprising tracking
start means responsive to an output of said second means indicative of
disappearance of synchronizing signal for initialize said tracking adjust
means and said third means.
4. The auto-tracking system claimed in claim 2 or 3, wherein said tracking
adjust means causes said servo means to change said phase difference by a
predetermined amount in a direction from the minimum value of a
predetermined variable range thereof to the maximum value.
5. The auto-tracking system claimed in claim 2 or 3, wherein said tracking
adjust means causes said servo means to change said phase difference by a
predetermined amount in a direction from the maximum value of a
predetermined variable range thereof to the minimum value.
6. The auto-tracking system claimed in any of claims 1 to 3, wherein said
second means comprises a periodicity measuring circuit having an input
connected to an output of said first means, a latch circuit having an
input connected to said periodicity measuring circuit, for delaying an
output signal from said periodicity measuring circuit by a predetermined
amount, a calculator having inputs connected to an output of said
periodicity measuring circuit and an output of said latch circuit, for
calculating a difference between the outputs of said periodicity measuring
circuit and said latch circuit to provide a variation of periodicity of
synchronizing signals, a second latch circuit having an input connected to
an output of said calculator, for providing a delay of a predetermined
amount, a comparator having inputs connected to said output of said
calculator and an output of said second latch circuit, for comparing a
current variation of synchronizing signal periodicity with a succeeding
variation of synchronizing signal periodicity and a tracking direction
setting circuit responsive to an output of said comparator for determining
a changing direction of tracking and informing the changing direction to
said tracking adjust means.
7. The auto-tracking system claimed in any of claims 1 to 3, further
comprising fourth means for detecting an FM envelope of said video signal
for a current signal field or frame and comparing it with an FM envelope
of a preceding video signal obtained at a preceding field or frame and a
switching circuit for connecting an output of said fourth means to said
tracking adjust means to cause said servo means to successively change
tracking by a predetermined amount such that the output level of said
rotary heads is maximized based upon a result of said comparison in said
fourth means and connecting an output of said second means to said
tracking adjust means to cause said servo means to predetermined change
tracking by the predetermined amount such that the periodicity variation
is minimized after said comparison in said fourth means indicates
equality.
8. The auto-tracking system claimed in claim 6, wherein said second means
comprises a periodicity measuring circuit having an input connected to an
output of said first means, a latch circuit having an input connected to
said periodicity measuring circuit, for delaying an output signal from
said periodicity measuring circuit by a predetermined amount, a calculator
having inputs connected to an output of said periodicity measuring circuit
and an output of said latch circuit, for calculating a difference between
the outputs of said periodicity measuring circuit and said latch circuit
to provide a variation of periodicity of synchronizing signals, a second
latch circuit having an input connected to an output of said calculator,
for providing a delay of a predetermined amount, a comparator having
inputs connected to said output of said calculator and an output of said
second latch circuit, for comparing a current variation of synchronizing
signal periodicity with a succeeding variation of synchronizing signal
periodicity, a tracking direction setting circuit responsive to an output
of said comparator for determining a changing direction of tracking and
informing the changing direction to said tracking adjust means and a
circuit responsive to an absence of a synchronizing signal to cause said
tracking direction setting circuit to fix the changing direction of
tracking.
9. An auto-tracking system for a video tape recorder, comprising:
means for controlling a dynamic positional relationship between rotary
video heads and a running magnetic tape into an optimum tracking position;
means for separating synchronizing signals in the video signals on the
running magnetic tape reproduced via the rotary video head; and
means for measuring a present cycle variation in the synchronizing signals
corresponding to a present tracking position determined by said tracking
control means, comparing the measured present cycle variation with a
preceding cycle variation in the synchronizing signals corresponding to a
preceding tracking position determined by said tracking control means and
setting a tracking correction direction which reduces the cycle variation
in the synchronizing signals based upon the comparison, said tracking
control means enabling successive shifting of the tracking position by a
predetermined amount in accordance with the tracking correction direction
set by said measuring means until the cycle variation in the synchronizing
signals is minimized to obtain the optimum tracking position.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an auto-tracking system for a helical scan
type magnetic recording/reproducing apparatus which necessitates tracking
adjustment during reproduction.
One of conventional auto-tracking system for helical scan type magnetic
recording/reproducing apparatus is disclosed in U.S. Pat. No. 4,613,914.
In the conventional arrangement disclosed in this patent, an envelope level
of reproduced signal is detected and the running phase of magnetic tape is
controlled such that the envelope level of the reproduced signal becomes
maximum after detection is effected roughly and then finely.
For high density recording using azimuthal recording method employed in a
home-use video tape recorder (VTR) of VHS or Beta type, and, particularly,
in a long time mode of operation thereof, however, there arises a problem
in accuracy of auto-tracking because the envelope level is greatly
affected by cross-talks between adjacent tracks.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an auto-tracking system
for a helical scan type magnetic recording/reproducing apparatus, which
achieves an optimum tracking with minimum jitter, without being affected
by cross-talks between adjacent tracks on a recording medium.
In order to achieve the above object, according to the present invention,
the fluctuation of periodicity of a synchronizing signal obtained by
demodulating an FM envelope signal is measured and the tracking is
adjusted automatically by varying tracking phase such that the measured
periodicity fluctuation becomes minimum.
In a reproduction in a reverse tracking, it is impossible to know a
direction of tracking correction since no synchronizing signal is
detected, even if tracking is changed slightly.
In such case, according to the present invention, the technique disclosed
in the aforementioned U.S. Patent is employed to roughly adjust the
tracking by using the FM envelope level and, after a synchronizing signal
is detected, the tracking is adjusted in a direction in which the
periodicity fluctuation is minimized.
Alternatively, the tracking phase is varied in only either direction from
the minimum of a variable tracking phase range to maximum or from maximum
to minimum until a synchronizing signal is detected, and, after detected,
the tracking is adjusted in the direction in which the periodicity
fluctuation reduces, in the same manner as above. That is, according to
the present invention, synchronizing signal is obtained from video signal
reproduced by a rotary video head and a periodicity fluctuation of the
synchronizing signal is measured, upon which the tracking is automatically
adjusted. Thus, an optimum tracking is obtained without any interference
due to cross-talks between adjacent tracks.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block circuit diagram of an automatic tracking system according
to an embodiment of the present invention;
FIG. 2 is a block circuit diagram showing details of a periodicity
detection circuit in FIG. 1;
FIG. 3 is a block circuit diagram of another embodiment of the present
invention;
FIG. 4 is a block circuit diagram of a still further embodiment of the
present invention; and
FIG. 5 is a block circuit diagram showing details of a periodicity
detection circuit in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will be explained with reference to
FIG. 1. In FIG. 1, reference numerals 1 and 2 indicate rotary video heads,
3 a cylinder on which the heads 1 and 2 are mounted, 4 a head position or
phase detector, 5 a magnet, 6 a cylinder motor mounting the magnet 5, 7 a
magnetic tape, 8 a control signal detector, 9 a servo circuit, 10 a
capstan motor, 11 an amplifier, 12 an FM envelope signal detection
circuit, 13 a level comparator circuit, 14 a switch timing circuit, 15 a
switch, 16 a signal processing circuit, 17 a synchronizing signal
separation circuit, 18 a periodicity detection circuit, 19 a circuit for
determining a completion of tracking adjustment, 20 a tracking adjust
circuit, and 21 a capstan motor shaft.
The rotary video heads 1 and 2 with different azimuth angles from each
other are arranged on the rotatable cylinder 3 with a phase difference of
180.degree. to alternatively record signals on or reproduce signals from
the magnetic tape 7. An axis of the rotary shaft of the cylinder 3 is
common with that of the cylinder motor 6, so that the cylinder 3 rotates
together with the shaft of the cylinder motor 6. The cylinder motor 6 is
controlled by the servo circuit 9. The magnet 5 is actually located on the
cylinder motor shaft although it is shown on the motor 6 for illustration
purpose, so that it rotates in synchronism with the rotary video heads 1
and 2. When the magnet 5 passes through the head position detector 4, the
head position detector 4 generates an electrical signal which represents
rotational phases of the rotary video heads 1 and 2 and is supplied to the
servo circuit 9 to control the rotational phase of the cylinder motor 6.
The servo circuit 9 is further supplied with a control signal from the
control singal detector 8 to drive the capstan motor 10 at a constant
speed. The magnetic tape 7 is in pressure-contact with the capstan motor
shaft 21 with an aid of a pinch roller not shown and runs by a distance
proportional to a rotation number of the capstan motor shaft 21.
As mentioned, the control signal detector 8 reproduces control signals
recorded on the magnetic tape 7 by the rotary video head 1 or 2 to
indicate track position.
During recording, the servo circuit 9 controls the capstan motor 10 so as
to rotate at a predetermined constant speed and, during reproduction,
controls the phase of the magnetic tape 7 through the capstan motor 10 and
the capstan motor shaft 21 by using the control signals detected at the
control signal detector 8, so that the phase relationship between the
rotary video heads 1 and 2 and the magnetic tape 7 at the time of
recording can be recovered.
When the apparatus used for recording is identical to that used for
reproduction, no problem arises with regard to the reproduction. When
these apparatus are not identical, the phase relationship between the
rotary video heads 1 and 2 and the magnetic tape 7 during the recording is
not always consistent with that during the reproduction because the
physical positional relationship between the rotary video heads 1 and 2
and the control signal detector 8 may be different. Therefore, in order to
electrically compensate for such physical positional displacement, the
phase relationship between the rotary video heads 1 and 2 which are
controlled by the cylinder motor 6 and the magnetic tape 7 which is
controlled by the capstan motor 10 through the capstan motor shaft 21 is
varied by the tracking adjust circuit 20 to obtain an optimum reproduction
tracking.
An operation for obtaining the above mentioned optimum reproduction
tracking will be explained below.
It is assumed that the tracking adjust circuit 20 varies the phase
relationship between the rotary video heads 1 and 2 and the magnetic tape
7 in a direction in which tracking amount expressed by numeral value is
increased, that is, a (+) direction with respect to the optimum tracking
during recording or reproducing.
The FM modulated signals reproduced at the rotary video heads 1 and 2 are
amplified at the amplifier 11. The FM envelope signal detection circuit 12
detects peaks of the FM modulated signals from the amplifier 11 and
converts the detected signal peak levels into electrical voltages. The
voltage amplitude is compared at the level comparison circuit 13 with that
detected at one field or one frame prior thereto. This comparison result
is output to the switch timing circuit 14 and the switch 15 controlled by
the switch timing circuit 14. In the initial condition of the present
system, the switch 15 is assumed to be connected to the terminal a so that
an output of the level comparison circuit 13 is inputted into the tracking
adjust circuit 20.
The tracking adjust circuit 20 controls the servo circuit 9 in such a
manner that when the output of the level comparison circuit 13 is large
with respect to an optimum tracking the tracking is varied in the (+)
direction and when such is small the tracking is varied in a (-)
direction.
The same operations are repeated. When the output of the level comparison
circuit 13 alternates large and small with respect to the optimum tracking
every time when the tracking amount is varied, it is deemed that a
tracking condition in which the output obtained from the rotary video
heads 1 and 2 is maximized is obtained and, then, the switch 15 is
changed-over from the terminal a to a terminal b by the switch timing
circuit 14.
Further, assuming that the tracking is again varied in the (+) direction by
the tracking adjust circuit 20, the output signal of the amplifier 11 is
demodulated at the signal processing circuit 16, from which the
synchronizing signal separation circuit 17 separates the synchronizing
signals. The periodicity detection circuit 18 measures the periodicity of
the synchronizing signals obtained by the synchronizing signal separation
circuit 17, detects a variation of the synchronizing signal within the
same field and compares the same with a variation of the synchronizing
signal obtained in the prior field or the prior frame. The variation is
expressed by one of arbitrary 2 values, large and small with respect to
the prior variation, and is output to the tracking adjust circuit 20
through the switch 15. In a case when the variation is large with respect
to the prior variation, however, an output polarity of the tracking adjust
circuit 20 is made correspondent with that of the level comparison circuit
13 providing a small result and, when the variation is small, the output
polarity of the tracking adjust circuit 20 is made correspondent with that
of a large result of the level comparison circuit 13. Accordingly, when
the periodicity detection circuit 18 detects the small variation in
periodicity of the synchronizing signal, the tracking adjust circuit 20
changes the tracking direction to the (+) direction and, when the
periodicity detection circuit 18 detects the large periodicity variation,
the tracking adjust circuit 20 changes the tracking direction to the (-)
direction. Namely, when the periodicity variation in a present detection
is small, the tracking correction is made in the same as direction in the
previous tracking correction and, when the periodicity variation is large,
the tracking direction is made opposite to the previous tracking
correction.
The above operations are repeated. When the periodicity variation at the
periodicity detection circuit 18 begins to alternate between large and
small or no substantial difference is observed in the periodicity
variation every time when the tracking amount is varied, the fluctuation
of periodicity of the synchronizing signals is minimized. This fact is
determined by the adjust completion detector 19 as an optimum tracking
condition in which jitter is minimum, and the detector circuit 19 causes
the tracking adjust circuit 20 to terminate the tracking correction.
With the above series of operations, an optimum tracking condition is
automatically obtained.
The construction and operation of the periodicity detection circuit 18 will
be explained in further detail with reference to FIG. 2.
In FIG. 2 in which the same elements are designated with the same reference
numerals as in FIG. 1, respectively, a reference numeral 30 denotes a
periodicity measuring circuit, 31 and 33 latches, 32 a calculator, 34 a
level comparison circuit and 35 a tracking direction setting circuit.
The periodicity measuring circuit 30 measures the periodicity of
synchroniziang signals detected at the synchronizing signal separation
circuit 17. The measured data is stored in the latch 31 and is further
inputted in the calculator 32. The latch 31 outputs the data after a
predetermined time delay corresponding to one horizontal synchronizing
signal period. The calculator 32 calculates a difference between the data
from the periodicity measuring circuit 30 and from the latch 31, from
which the periodicity variation in the synchronizing signals is detected.
The calculation result is inputted to both the level comparison circuit 34
and the latch 33. The latch 33 receives the calculated data and outputs it
with a delay of the same period as that for the tracking change by the
tracking adjustment circuit 20 as explained above. The period of the
tracking modification (the delay time of the latch 33) is determined by
using one field or one frame as a unit. The level comparison circuit 34
compares the output magnitude of the calculator 32 with that of the latch
33 and calculates the periodicity variation in the synchronizing signals
before and after a modification of tracking. When the level comparison
circuit 34 results that the periodicity variation is small, the tracking
direction setting circuit 35 determines the direction of the tracking
correction as the same as in the previous correction and, when the
periodicity variation is large, the tracking direction setting circuit 35
determines the direction of the tracking correction as being opposite to
that in the previous correction. The determination is supplied to the
tracking adjust circuit 20 through the switch 15.
The calculator 32 in the above embodiment may calculate a difference in one
horizontal synchronizing signal period or may calculate an average value
by summing up differences in several horizontal synchronizing signal
periods.
Further, when a comparison result in the level comparison circuit 34 shows
an equality between the outputs from the calculator 32 and from the latch
33 or shows a difference which is as small as negligible detection errors,
the same direction of tracking correction as in the previous correction is
selected to accommodate to a marginal value of the optimum tracking,
noises or measurement errors.
Another embodiment of the present invention will be explained with
reference to FIG. 3.
In FIG. 3 in which the elements having the same functions as those in FIG.
1 are designated with the same reference numerals as in FIG. 1, reference
numerals 40 and 41 depict rotary audio heads, 42 an amplifier, 43 an FM
envelope signal detection circuit, 44 a non-recording circuit, and 45 a
switch.
The audio FM modulated signals recorded on the magnetic tape 7 are
reproduced via the rotary audio heads 40 and 41, amplified at the
amplifier 42 and peak-detected at the FM envelope signal detection circuit
43. An output signal from the FM envelope signal detection circuit 43
indicates the level of reproduced audio FM modulated signal which
corresponds to the detection of the output level of the rotary video heads
1 and 2 as voltage signals at the FM envelope signal detection circuit 12
as explained previously.
The non-recording circuit 44 detects an absence of FM modulated audio
signal when voltage level at the FM envelope signal detection circuit 43
is lower than a predetermined level even if the tracking is modified by
the tracking adjust circuit 20, and the circuit 44 controls the switch 45
to change-over itself to a terminal d. When the voltage level at the FM
envelope circuit 43 exceeds the predetermined level the non-recording
circuit 44 decides a presence of audio FM modulated signals recorded and
changes-over the switch 45 to a terminal c.
When the switch 45 is connected to the terminal d, an optimum tracking is
automatically obtained through the same series of operations as explained
in connection with the above embodiment in FIG. 1.
Further, output signal of the FM envelope signal detection circuit 43
obtained when the switch 45 is connected to the terminal c functions
similarly to that of the FM envelope signal detection circuit 12 since
operation on the FM modulated video signal is merely replaced with the
operation on the FM modulated audio signals. Thus, it is possible to
obtain an optimum tracking automatically as in the same manner as in the
previous embodiment.
Still another embodiment of the present invention will be explained with
reference to FIG. 4. In FIG. 4, in which the elements having the same
functions as those in FIGS. 1 and 3 are designated with the same reference
numerals as in FIGS. 1 and 3, a reference numeral 50 indicates a
periodicity detection circuit, 51 an initializing circuit and 52 a
tracking start circuit.
When the magnetic tape 7 is newly loaded and a reproduction is started or
when the state of the reproduced signal at the periodicity detection
circuit 50 changes from one indicating that there is a synchronizing
signal contained in the reproduced signal to one indicating that there is
no synchronizing signal contained therein, the tracking start circuit 52
generates a command signal to the initialization circuit 51 and the
tracking adjust completion circuit 19 to initialize a tracking value in
the tracking adjust circuit 20 and the tracking adjust completion circuit
19. The initialization values in this initializing step is determined at
the maximum or the minimum value of the variable tracking range.
The servo circuit 9 begins to operate with the data signals from the
initialized tracking adjust circuit 20 and the rotary video heads 1 and 2
begin to reproduce video signals recorded on the magnetic tape 7. A
synchronizing signal is separated from the reproduced video signal by the
separation circuit 17 through the amplifier 11 and the signal processing
circuit 16.
The periodicity detection circuit 50 determines a presence or absence of
the synchronizing signal through the periodicity measurement of the
synchronizing signal.
When the presence of the synchronizing signals is determined, the tracking
adjust circuit 20 operate so as to minimize the synchronizing signal
fluctuation at the periodicity detection circuit 50.
When the absence of synchronizing signal is determined, the tracking is
changed in one direction in the tracking adjust circuit 20 until the
synchronizing signals is detected. The one direction in this instance
means a direction toward the minimum value when the initial tracking value
set by the tracking adjustment circuit 20 is at the maximum value within
the variable tracking range, or a direction toward the maximum value when
the initial tracking value is set at the minimum value in the range. The
above operation eliminates such condition that the correcting direction of
tracking can not be determined when no synchronizing signals are detected
due to the fact that a periodicity fluctuation in the synchronizing signal
does not contain any change even if the tracking amount is varied.
FIG. 5 shows a detailed block circuit diagram of the periodicity detection
circuit 50. In FIG. 5, in which the elements having the same functions as
those in previous embodiments are designated with the same reference
numerals as in the previous embodiments, a reference numeral 55 indicates
a synchronizing signal detecting circuit, and 56 a tracking direction
setting circuit.
The synchroniziang signal detecting circuit 55 measures the period of
synchronizing signal and, when the synchronizing signals are detected
regularly within a time of few microseconds of a standard period defined
in NTSC or PAL standard, it is determined that there are synchronizing
signals. When an abnormally short or long period compared with such time
as few microseconds is measured, it is determined to be noise and the
synchronizing signals are determined to be absent. In the latter case, the
tracking direction setting circuit 56 is fixed to the correcting direction
of tracking.
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